Vulcanization treatments



United States Patent 3,061,594 VULCANIZATION TREATMENTS Gerard W.Kuckro, Fairfield, Conn., assignor to General Electric Company, acorporation of New York No Drawing. Original application Nov. 23, 1956,Ser. No. 623,767, now Patent No. 2,922,804, dated Jan. 26, 1960. Dividedand this application Apr. 30, 1959,

Ser. No. 809,898

Claims. (Cl. 260-795) This invention relates to vulcanization oraccelerator compounds for effecting the cure of the various syntheticand natural rubbers; more particularly, the invention relates to anaccelerator compound for curing butyl rubber. This application is adivision of my application Serial No. 623,767, filed November 23, 1956,now US. Patent No. 2,922,804.

In effecting the cure of the various rubbers or elastomers, vulcanizingagents and/ or accelerating agents (hereinafter referred to ascross-linking agents) to promote cross-linking of the macromoleculesforming the uncured composition are introduced to the mix which is thennormally subjected to heat under pressure. Since the various natural andsynthetic elastomers vary considerably in degree of saturation,cross-linking agents which will be satisfactory for a highly unsaturatedelastomer, such as natural rubber, will be unsatisfactory for a slightlyunsaturated -elastomer such as butyl rubber, and vice versa.

In addition to effecting the cure of the rubber, crosslinking agentshave a considerable effect on the properties of the cured materialitself. Thus, the slightly unsaturated butyl rubber has for many yearsbeen cured by a combination consisting of sulfur,2-mercaptobenzothiazole and tetramethylthiuram disulfide when the finalproduct is used for inner tubes. However, when butyl rubber is to beused as insulation on wire, its life must be increased by a factor of 10over its use in inner tubes and the curing system above-described forinner tubes is totally inadequate. Where electrical insulation is theend use, the preferred cross-linking agents are p-quinonedioxime anddibenzoyl p-quinonedioxime. Neither of these latter cross-linking agentsis entirely satisfactory, for p-quinonedioxime is so active thatscorching. is apt to result while its derivative, dibenzoylp-quinonedioxime, is not sufficiently active to bring about a high stateof cure.

It is an object of the present invention to provide crosslinking agentswhich can readily bring about the curing of weakly unsaturatedelastomers.

It is another object of the invention to provide a vulcanizable rubbercomposition which includes a cross-linking agent which will effect thecure of the composition without scorching it.

It is another object of the invention to provide a method of producingvulcanized rubber by means of a new and novel cross-linking agent.

In accordance with one of its aspects, this invention is directed to across-linking agent of the structure in which M is selected from thegroup consisting of lead, zinc, tellurium, bismuth, and cadmium; and Xis selected from the group consisting of hydrogen, halogen, alkyl, aryl,aralkyl, and alkaryl.

While the above structure includes a benzene nucleus, the compound isalso a satisfactory cross-linking agent in polynuclear form such aswould be produced by substitution of a naphthalene or anthracene nucleusfor the benzene nucleus illustrated. In its preferred form, theinvention is directed to a benzene nucleus, X is hydrogen, and

Patented Oct. 30, 1962 M is lead. This preferred compound has theformula ON-QO-Pb-OH which may be considered as the basic form of theinvention, While other metals may be substituted for lead and thebenzene nucleus may be polynuclear or have substituent groups attachedthereto, the final result is to reduce the activity of the cross-linkingagent. The lead compound structurally depicted above will hereinafter bereferred to as basic lead p-nitrosophenolate.

Basic lead p-nitrosophenolate may be readily prepared by reacting diluteaqueous solutions of p-nitrosophenol, sodium hydroxide, and leadnitrate, two moles of sodium hydroxide and one of lead nitrate beingpresent for each mole of p-nitrosophenol. These components will react atroom temperature to precipitate out basic lead p-nitrosophenolate inabout yield.

Composite samples of the dried precipitate formed by the above reactionhave analyzed 21.58% carbon, 1.44% hydrogen, 3.52% nitrogen, and 59.22%lead. These percentage compositions are quite close to the theoreticalcompositions computed for basic lead p-nitrosophenolate showing that ahigh degree of purity is attained in the final product.

, A final product containing metals other than lead may be produced bysubstituting the nitrates of such metals for lead nitrate in the abovereaction. Thus, the nitrates of zinc, tellurium, bismuth, and cadmiummay be substituted for lead nitrate to give the corresponding meta-lp-nitrosophenolates. Likewise, the corresponding naphthalene,anthracene, and other polynuclear compounds may be substituted forp-nitrosophenol to produce the corresponding polynuclear end products.While sodium hydroxide was specified in the above description, it isobvious that other hydroxides, such as potassium hydroxide, would givethe same result and such variations are well within the realm of askilled chemist.

After the precipitated lead p-nitrosophenolate has been dried, it isready for compounding with uncured rubber prior to the formingoperations such as extrusion or molding and vulcanization. Dependingupon the characteristics of the uncured rubber, the cross-linking agentsof this invention are added in the proportion of 0.5% to 10% by weightand further compounding and working is performed in the conventionalmanner as by treatment in a Banbury mixer and milling prior to formingand vulcanization. Reducing conditions are provided by 0.25% to 6% byweight of sulfur, selenium, or tellurium. A preferred reducing agent isabout 1% by weight of sulfur.

While the cross-linking agents of the present invention olfer advantagesin the vulcanization of butyl rubber which cannot be achieved by the useof other cross-linking agents, they may also be used to vulcanize otherrubbers such as natural rubber, silicone rubber, the synthetic nitrilerubbers, and other synthetic rubbers derived from butadiene or isoprene.

The cross-linking agents of this invention may be mixed with othercross-linking agents and in some cases the mixture confers properties onthe final vulcanized rubber which are superior to the propertiesproduced by either agent used alone. Thus, an excellent cross-linkingagent is formed from about a 50-50 mixture of basic leadp-nitrosophenolate and lead mercaptobenzothiazole.

For ease of handling, the cross-linking agents of this invention may bemixed with an inert substance such as polyisobutylene. A satisfactorymixture of this type is 5% to 95 by weight of basic leadp-nitrosophenolate and 5% to 95% by weight of polyisobutylene. It isdesirable to use as small a proportion of polyisobutylene as possiblecommensurate with easy and safe handling of the cross-linking agent.Other cross-linking agents may also be present in the polyisobutylenemixture. A useful mixture containing two cross-linking a-gents comprisesabout 55% by weight of basic lead p-nitrosophenolate, about 40% byweight of lead mercaptobenzothiazole, and about 5% by weight ofpolyisobutylene.

The foregoing invention is directed generally toward a cross-linkingagent having a structure in which a metal is connected to a hydroxygroup through one valence bond and through an oxygen atom to a ringhaving a nitroso group in the para position by the other valence bond;particularly, the invention is directed toward lead and a benzene ringin this type of structure. It is obvious that this nucleus structure canhave many derivatives which incorporate such nucleus therein. Therefore,it is intended that this invention be limited only as may benecessitated by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. The method of producing vulcanized rubber which comprises efiectingthe vulcanization of a composition selected from the group consisting ofuncured butyl rubber, natural rubber, silicone rubber, synthetic nitrilerubber, and rubbers derived from butadiene and isoprene by a compound inwhich a metal selected from the group consisting of lead, zinc,tellurium, bismuth, and cadmium is connected to a hydroxy group throughone valence bond and through an oxygen atom to a benzene nucleus havinga nitroso group in the para position by another valence bond underreducing conditions provided by a member selected from the groupconsisting of sulfur, selenium and tellurium.

2. The method of claim 1 wherein vulcanization is efiected by a compoundof the structure and the reducing conditions are provided by sulfur.

3. A vulcanizable composition comprising a composition selected from thegroup consisting of uncured butyl 4. rubber, natural rubber, siliconerubber, synthetic nitrile rubber, and rubbers derived from butadiene andisoprene and 0.5% to 10% by weight of a compound of the structuralformula ore-@o-m-on in which M is selected from the group consisting oflead, zinc, tellurium, bismuth, and cadmium.

4. A vulcanizable composition as claimed in claim 3 wherein the uncuredcomposition is butyl rubber.

5. A vulcanizable composition as claimed in claim 3 wherein M is lead.

6. A vulcanizable composition as claimed in claim 5 wherein the uncuredcomposition is butyl rubber.

7. A vulcanizable composition comprising uncured silicone rubber and0.5% to 10% by weight of a compound of the structural formula in which Mis selected from the group consisting of lead, Zinc, tellurium, bismuth,and cadmium.

8. A vulcanizable composition as claimed in claim 7 wherein M is lead.

9. A composition of matter comprising 5% to 95% by weight of thestructure the remainder being polyisobutylene.

10. A composition of matter comprising about by weight of a compoundhaving the structure oN-Qo-m-on about 40% by weight of leadmercaptobenzothiazole, and about 5% by weight of polyisobutylene.

References Cited in the file of this patent UNITED STATES PATENTS2,444,546 Walsh July 6, 1948

1.THE METHOD OF PRODUCING VULCANIZED RUBBER WHICH COMPRISES EFFECTINGTHE VYLCANIZATION OF A COMPOSITION SELECTED FROM THE GROUP CONSISTING OFUNCURED BUTYL RUBBER, NATURAL RUBBER, SILICONE RUBBER, SYNTHETIC NITRILERUBBER, AND RUBBERS DERIVED FROM BUTADIENE AND ISOPRENE BY A COMPOUND INWHICH A METAL SELECTED FROM THE GROUP CONSISTING OF LEAD, ZINC,TELLURIUM, BISMUTH, AND CADMIUM IS CONNECTED TO A HYDROXY GROUP THROUGHONE VALENCE BOND AND THROUGH AN OXYGEN ATOM TO A BENZENE NUCLEUS HAVINGA NITROSO GROUP IN THE PARA POSITION BY ANOTHER VALENCE BOND UNDERREDDUCING CONDITIONS PROVIDED BY A MEMBER SELECTED FROM THE GROUPCONSISTING OF SULFUR, SELENIUM AND TELLURIUM. 7.A VULVANIZABLECOMPOSITION COMPRISING UNCURED SILICONE RUBBER AND 0.5% TO 10% BY WEIGHTOF A COMPOUND OF THE STRUCTURAL FORMULA